Field of the Disclosure
The present invention relates in general to abrasive wheels and, in particular, to a system, method and apparatus for abrasive articles having improved work of fracture properties.
Description of the Related Art
Phenolic-based resins used to manufacture grinding wheels are inherently brittle materials that are subject to failure due to the probability of defects within the part. Reinforcements are therefore used in most wheels to preclude brittle and catastrophic failure.
One such reinforcement is a fiber glass web or fabric of various weights and styles. The webs are designed to increase the fracture toughness or work of fracture of the wheel, which ultimately prevents the explosive release of wheel fragments in the event that the wheel breaks during use. The web comprises a plurality of individual yarns or strands woven into a 0°/90° open structured fabric. Once the fabric is formed, it is dipped in a phenolic resin and subsequently dried and cured to form a thermosetting coating. Once the coating is cured to the desired level, the web is wound into a roll for easy storage until needed. The final step in preparing the web for use in the wheel is unwinding the roll and cutting individual discs having the desired dimensions. The process is labor and time intensive, generates significant waste and is therefore expensive. This basic process has been used for more than 50 years.
Chopped strand fibers also have been used to reinforce resin-based grinding wheels. The chopped strand fibers may comprise fiber bundles or strands, typically 3 to 4 mm in length and include many individual filaments. The number of filaments can vary depending on the manufacturing process but typically is in a range of about 400 to 6000 filaments per bundle or strand. The filaments are held together by an adhesive known as a sizing, binder, or coating that should ultimately be compatible with the resin matrix. The sizing comprises less than 2 wt % of the fiber. The amount of sizing or coating is limited by the fiber manufacturing processes used to make direct sized yarn or chopped strand products. One example of a chopped strand fiber is referred to as 183 Cratec®, available from Owens Corning.
Incorporation of chopped strand fibers into a dry grinding wheel mix is generally accomplished by blending the chopped strand fibers, resin, fillers, and abrasive particles for a specified time and then molding, curing, or otherwise processing the mix into a finished grinding wheel.
Traditional chopped strand fiber reinforced wheels can suffer from a number of problems, including lower strength, poor grinding performance and shorter wheel life, presumably due to incomplete dispersal of the filaments within the chopped strand fiber bundle, poor adhesion between the wheel matrix resin and the chopped strand bundle, fiber length degradation, or a combination of all of these. However, another deficiency for chopped strand reinforcements can be their low fracture toughness contribution to the composites or wheels relative to glass fiber webs. There is a need, therefore, for improved reinforcement techniques for abrasive processing tools without compromising performance.